1. Field of the Invention.
The present invention is directed toward the field of reply rate limiting, and particularly toward the field of limiting the number of replies by a transponder to signal inquiries from an external source.
2. Background, Objects and Description of the Prior Art.
Communication between air traffic control ground stations and aircraft transponders has been in practice for many years. Communication typically takes place along FAA specified radio frequency channels in the thousand Megahertz range, e.g., 1030 and 1090 MHz. The transponders employed are radio systems including one or more receivers and transmitters which respond automatically to receipt of predetermined signal inquiries which request a response of predetermined character, according to one of a number of preestablished signal formats requesting specified information, subject to rate limitations.
The air traffic control ground stations repeatedly transmit such signal inquiries with a rotating ground station antenna. However, the aircraft transponder is limited in the number of replies it can make over time due to increased radio interference, power supply restraints, and transponder heat production. In view of these restraints, there is an upper limit as to the number of allowable responses per time interval a transponder can make. In particular, whereas high response rates may be permitted over short time intervals, average response rates over longer time intervals must be lower.
Current aircraft transponders generally perform reply rate limiting by reducing the sensitivity of the transponder receiver, according to known hardware circuit techniques.